1. Field of the Invention
This invention relates to a process for producing a silicone latex.
2. Description of Art
Silicone latex as a general class of material is known, but has not been widely used. Various emulsions of silicone polymers, such as polydiorganosiloxanes, are known and are commercial products. An emulsion containing methylpolysiloxane and silica as an antifoam agent was described by Currie as early as 1952 in U.S. Pat. No. 2,595,928. Other emulsions of siloxanes are described by Findlay and Weyenberg in U.S. Pat. No. 3,294,725 and Hyde et al. in U.S. Pat. No. 2,891,920.
In U.S. Pat. No. 3,098,833, a process for preparing a catalyzed organopolysiloxane emulsion is described. The organopolysiloxane is defined as containing hydrogen atoms and/or hydroxyl radicals. This emulsion is defined as useful for a treating bath for cellulosic materials to make them water repellent. The shelf-life of these catalyzed aqueous organopolysiloxane emulsions is defined as in the order of more than 4 to 5 days.
U.S. Pat. No. 3,355,406 described silicone rubber latexes reinforced with silsesquioxanes. These latexes are made by making a colloidal suspension of a hydroxyl containing linear siloxane polymer, then adding the colloidal silsesquioxane, and optionally crosslinker and catalyst. These latexes are defined as stable upon standing but when applied to a substrate and the water evaporated, a film of silicone rubber or plastic is left behind.
U.S. Pat. No. 3,445,415 describes a method for making an organic latex adding organic monomer to a colloidal suspension containing a free radical catalyst, then polymerizing the organic monomer. The silsesquioxane serves as the site for the polymerization of the organic monomer.
The abstract of Japanese Kokai No. 75-35,225 in Chemical Abstracts, Volume 83, 1975, page 148, 81560w describes a composition comprising an organopolysiloxane emulsion, a hardener, and an aqueous emulsion containing organohydrodienepolysiloxane and diorganopolysiloxane with hydroxy end groups. This composition is described as being used to impregnate asbestos sheet base gaskets.
U.S. Pat. No. 3,706,695 describes a silicone emulsion prepared from hydroxyl containing polydiorganosiloxane, carbon black, a metallic salt of a carboxylic acid and an alkoxy silane of the formula RSi(OR').sub.3. The emulsion cures to a silicone rubber when the emulsion is used within periods of up to two weeks or more after preparation, but is not curable after long storage and requires regeneration by adding more alkoxysilane or organometallic catalyst or both.
From these references, it has been known prior to this application, that silicone latexes could be prepared from hydroxyl polydiorganosiloxane, alkoxysilanes or siloxanes containing silicon-bonded hydrogen atoms and a metallic salt of a carboxylic acid. These silicone latexes or emulsions are curable by removing the water at room temperature or by heating.
U.S. Pat. No. 3,445,420 describes a heat curable composition comprising a vinyl organosilicon polymer, an organosilicon compound containing SiH, a platinum catalyst and an acetylenic compound. These compositions are described as stable at low temperatures and curable by heating. These curable compositions can be dispersed in a volatile diluent including organic solvents and water. This patent teaches that water can be used as the diluent under conditions where there is little hydrolysis of the SiH bonds. This patent also teaches that the volatile diluent shows a strong inhibition to cure but that cure will occur when the diluent is evaporated.
In U.S. Pat. No. 3,900,617, there is described an aqueous emulsion treating bath which comprises a vinyl chain-stopped polyorganosiloxane, an organic hydrogen polysiloxane and a platinum catalyst. This patent describes the water as acting as an inhibitor for the platinum catalyzed vinyl/SiH reaction. For storage purposes, this patent states that it is best to prepare two separate emulsions, keeping the organohydrogenpolysiloxane component and the platinum catalyst separated.